1. Field of the Invention
The present invention relates generally to computed tomography (CT), and more particularly to a user interface for displaying an enhanced CT scan image.
2. Background
In conventional analysis of CT images, a radiologist visually inspects each slice of a CT scan, using his or her expertise to identify abnormalities and to distinguish them from normal structures. The task can be made easier by storing the scan image on a computer and providing a user interface that allows the user to move rapidly between slices and visualize the structures in different ways. However, the process is time consuming and must be performed with great care to avoid overlooking abnormalities.
To replace some or all of the work of the radiologist, Computer Assisted Detection (CAD) software has been designed to analyze the scan image and to detect potential lesions. The detection of a lesion can be performed semi-automatically, with some interaction with the radiologist, or automatically, involving no interaction beyond the selection of the image to be analyzed. For example, the applicant's MedicHeart™, MedicLung™, and MedicColon™ diagnostic software perform semi-automatic diagnosis using CT scans of the heart, lung, and colon, respectively.
In practice, the results of CAD can be checked by a radiologist as a safeguard. If the software is used as the ‘first reader’, the radiologist generally only verifies the results produced by the software and does not analyze the original CT scan. To be effective as a ‘first reader’, the software needs both high sensitivity (i.e., a low percentage of missed lesions) and high specificity (i.e., a low percentage of false positives), because the radiologist may make medically important decisions based on the results. Using software as a ‘first reader’ can save substantial time of the radiologist, though achieving both high sensitivity and high specificity can pose a significant challenge.
Alternatively, the software can be used as a ‘second reader’, where the radiologist makes a preliminary diagnosis based on the original images, and then runs the software as a check for any missed lesions. When used as a ‘second reader’, the software typically does not save time, but can assist the radiologist in making better diagnoses. The software does not need to have particularly high sensitivity or specificity, so long as it leads to more accurate diagnoses than an unassisted radiologist. Used in this way, the software is analogous to a spelling or grammar checker for word-processing. For instance, the software merely draws the user's attention to oversights, rather than replacing the actions of the user.
What is needed is a user interface for analysis of CT scans that does not need to be as accurate as ‘first reader’ software and saves more time than ‘second reader’ software.
PCT patent application WO 03/077203 discloses a user interface that allows corresponding areas from different scans to be displayed side-by-side.
A further problem is that many CAD algorithms rely on a predefined set of parameter ranges for detection of abnormalities. For example the Agatston method, as originally described in ‘Quantification of coronary artery calcium using ultrafast computed tomography’, Agatston A S, Janowitz W R, Hildner F J et al., J Am Coll Cardiol 1990 15:827–832, applies a threshold of 130 Hounsfield units (HU) to the CT image, and identifies all pixels above that threshold as containing calcium. A scoring system is then used to rate the severity of the calcification, based on the number of pixels above the threshold multiplied by a weight based on the highest intensity within the calcification. If the highest intensity is between 130 and 200 HU, then the weight is 1; if between 200 and 300 HU, the weight is 2; and if over 300 HU, the weight is 3. The values of the threshold and the weights are based on empirical studies of coronary scans and the subsequent outcome for the patients. However, there is continuing debate as to which parameter ranges give the most accurate results. Different ranges may be appropriate for different scan images.
U.S. Pat. No. 6,058,322 discloses an interactive user modification function in which software displays detected microcalcifications and a user may then add or delete microcalcifications. The software modifies its estimated likelihood of malignancy accordingly.